The present invention relates to a composition for deactivating the surface of concrete or mortar, a process of obtaining a concrete or mortar deactivated with the help of this composition and their uses.
Deactivated concrete or mortar is a material in which the superficial cement has been eliminated, leaving granulates to appear in relief thereby permitting obtaining a certain aesthetic effect.
Thus, for usual concretes, the surface appearance is determined by the quality of the mold (vertical surfaces or mold foot) or by the quality of finish of the surfaces obtained by floating (horizontal surfaces). The appearance which results is that of a smooth or almost smooth concrete whose color is essentially determined by that of the cement and the fines. For certain applications such as road maintenance and facade elements, it is interesting to provide concretes which, whilst maintaining their structural performance, have a widened variety of appearances.
In the industry of prefabrication of ready to use concrete, the methods that are most useful to cause the granulates to appear consist either in treating the surface of the concrete (after hardening and possible demolding) by using mechanical means, or by deactivating the surface of the concrete during the period of hardening by using chemical retardants.
Concretes adapted to be deactivated must preferably have a granulometric distribution of the particulate granulates to the end of ensuring regularity of their appearance when these latter are visible at the surface.
Once these precautions are taken, deactivation consists in distributing over the exposed surface of the fresh concrete or on the surface of the mold adapted to receive the fresh concrete, a compound having retardant effect on the setting of the cement. The compound must be in a concentration such that its retardant effect is within the top millimeters of depth. Thus, only the mortar near the surface of the concrete (namely the concrete skin) will have a different setup time. The body of the concrete itself will set normally. When the body of the concrete is sufficiently hardened, cleaning its surface with water (possibly under pressure)xe2x80x94or xe2x80x9csoakingxe2x80x9dxe2x80x94is carried out. Not having set up, the mortar is eliminated, and the granulates appear whilst remaining secured to the assembly.
It is thus necessary to formulate balanced deactivating compositions, which is to say such that the active principle (the retardant) penetrates the mortar at most a distance equal to one-third of the largest diameter of the granulatesxe2x80x94if not they loosenxe2x80x94and however give rise, over this distance, to a retardation of setting sufficiently long to let the body of concrete harden and thereby permit the cleaning of the surface of the concrete without damaging the body.
The compositions already on the market comprise a setting retardant, most often associated with a so-called xe2x80x9ccuringxe2x80x9d product which is generally a resin made solvent in an aliphatic solvent, forming a film which limits the drying of the concrete before xe2x80x9csoakingxe2x80x9d.
These compositions thus have the drawback of including volatile solvents which are undesirable according to recent directives on admissions of volatile organic compounds (VOC) in the environment.
Among the retardants, can be cited the gluconates, or else cyclic aminoplast resins described in the patent FR2 722 777.
More recently there have been used aqueous compositions of latex base of the type of styrene butadiene, playing the role of a curing agent, including a cyclic aminoplast resin as retardant and if desired applying the rheology, namely a thickener: cellulose ether or compound of the HASE type (emulsion, soluble in alkali, of a polymer with hydrophobic modification) to avoid running on inclined ground.
This thickener is of low concentration (less than 0.5% by weight) so that the composition will be sufficiently fluid to be sprayed.
Such compositions (see Table 1) sold in commerce, are arranged according to ranges of power (which is to say concentration of retardant) suitable for the usual sizes of granulates and to climatic conditions at the workplace because the temperature affects the setting of the cement and the speed of diffusion of the active principle.
However there will always remain a certain number of imponderables as to the climate, particularly during the time before washing, which is to say once the selected power is applied. As a consequence, the provided power is often not the best. If the temperature of the workplace or of the shop is higher than provided, setting is too rapid and it becomes impossible to wash the skin of the concrete, which is too hard. If the temperature is lower than provided, setting is too slow and the body of the concrete does not harden sufficiently rapidly to permit washing the surface in a reasonable time without it being damaged.
A first object of the invention is therefore to overcome the drawbacks connected to climatic imponderables, by providing a deactivating composition which permits selecting the power of deactivation independently of the external temperature during production of the concrete and independently of the duration of action of said composition before washing (xe2x80x9csoakingxe2x80x9d).
The deactivating composition according to the invention should be adapted to be applied by a conventional method such as spraying. The composition should moreover have a high viscosity to avoid possible running or accumulation in the low points, whilst promoting regular and homogeneous distribution over the surface of the concrete to be treated. However, spraying the compositions including rheology modifying agents (thickeners) is not easy.
A second object of the invention is thus to provide a homogeneous composition having rheological characteristics permitting on the one hand its spraying and on the other hand its application without running or accumulation.
These objects are achieved by the composition according to the invention, namely a deactivating composition for the surface of concrete or mortar comprising a retardant, water and if desired a Hydrophobically Modified Alkaline Soluble Emulsion polymer, abbreviated as HASE as a rheology modifying agent, characterized in that the retardant is a carboxylic acid and in that the concentration of HASE is greater than or equal to 0.5% by weight. Preferably, the concentration of HASE is comprised between 1 and 10% by weight, preferably between 5 and 6% by weight.
The combination of an HASE, in particular at such a concentration level, with a carboxylic acid in acidic form, and not in its salt form, permits surprisingly to obtain a deactivating composition with low viscosity, easy to spray, whose rheology does not change (by thickening) until contact with the surface of the concrete (exceeding a viscosity of 5,000 to 10,000 mPa""s, for example). There are accordingly no problems of running nor accumulation in low points. The deactivating composition according to the invention can even be used on vertical walls.
Thus, mixtures of sodium glucanate or cyclic aminoplast resins with several percent of HASE are too viscous to be sprayed.
The rheology modifier of the HASE type can be constituted either by homopolymers obtained from acrylic acid, methacrylic acid or acrylamide, or copolymers obtained from the same monomers with, in addition, acrylic esters in various proportions.
Preferably, the carboxylic acid has the general formula (I):
Formula (I):
R1 being H or xe2x80x94CH2xe2x80x94COOH
R2 being H or OH
R3 being H, CH3, xe2x80x94(CHOH)n-CH2OH, or xe2x80x94(CHOH)n-COOH
and n being a whole number from 1 to 3.
The retarder can particularly be selected from acidic acid, tartaric acid, citric acid, gluconic acid or lactic acid.
It has been discovered that in a preferred manner, the carboxylic acid is an a alcohol acid, which is to say that the carbon carrying the carboxylic acid function also carries a hydroxy group (case in which R2=OH in the formula (I) above).
The surprising character of the invention resides in the fact that when a combination is used of a carboxylic acid (most of the time generally known as a retarder) and a rheology modifying agent of the HASE type, in particular at a concentration greater than or equal to 0.5%, in a formula for deactivating the surface, the delay in setting of the skin of the concrete is practically invariable with temperature (particularly between about 5 and 40xc2x0 C.) and independent of the duration of washing of the concrete after spraying the deactivator. This gives to the composition according to the invention a very wide facility and flexibility of use, particularly at outside workplaces, and particularly in summer.
The composition according to the invention being an aqueous solution, it moreover has the advantage of not containing petroleum origin solvents. It cannot be implied in emission of VOC""s (volatile organic compounds) in the atmosphere according to the directive 1999/12/CE of the Council relative to the reduction of emissions of volatile organic compounds due to the use of organic solvents in certain activities and installations.
The present invention also relates to the process for the modification of the surface of concrete or mortar during its setting, consisting in applying a deactivating composition according to the invention in proportions of the order of 0.25xc2x10.05 liter per square meter of said surface, then washing with water this surface after a predetermined period.
The composition according to the invention can be used for the deactivation of concrete or mortar made with any type of cement, in particular cements of the type CEM I or CEM II.
This use is altogether appropriate at temperatures comprised between about 5 and 40xc2x0 C.